This invention relates generally to a method and apparatus for determining a force of a work tool as the work tool contacts a surface and, more particularly, to a method and apparatus for compensating for non-contact forces of the work tool to more accurately determine a contact force of a work tool.
Work tools are used in many situations in which it is desired to contact a surface in a carefully controlled manner. If too little force is applied upon contact, the work performed may be inefficient and non-productive. On the other hand, if too much force is applied, the surface being worked on, as well as the work tool itself, may be damaged.
Examples of work tools which must contact a surface to perform the desired work abound in many industries. For example, manufacturing and machining must use surface contacting work tools throughout the processes. The construction and earthworking industries must also use various types of surface contacting work tools. Service industries, such as industrial and commercial cleaning and maintenance, also employ different types of work tools which must contact surfaces to function.
Taking the construction and earthworking industries into consideration for exemplary purposes, work tools are often connected to work machines by way of controllable linkage assemblies. For example, wheel loaders and backhoe loaders are work machines which may use any of several different work tools, such as buckets, rollers, sweepers, and the like. These work tools must be used so that they contact a surface, e.g., a road, the ground and such, with certain desired forces. As a specific example, a wheel loader or backhoe loader having a sweeper attachment as a work tool must control the sweeper so that contact forces do not exceed desired limitations. The application of excessive force damages the work tool, thus resulting in costly loss of productive time.
Although the application of the proper force as the work tool contacts a surface is highly desired and necessary, it is quite difficult for an operator of a work machine, or even for typical automated processes, to accurately control the amount of force applied to the work tool as it contacts a surface. Furthermore, the required control of the force applied is very difficult to achieve at the moment of time that the work tool initiates contact with the surface. More specifically, it is difficult to monitor the force applied to a work tool and responsively determine the instant of time that the work tool contacts a surface so that control of the contact force takes place at the moment of contact.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for determining a contact force of a work tool is disclosed. The method includes the steps of determining at least one non-contact force exerted on the work tool, determining a calibration factor as a function of the at least one non-contact force, determining a contact being made between the work tool and a surface, and determining the contact force of the work tool with the surface as a function of the contact being made and the calibration factor.
In another aspect of the present invention an apparatus for determining a contact force of a work tool with a surface, the work tool being controllably attached to a linkage assembly, the linkage assembly being controllably attached to a work machine, is disclosed. The apparatus includes at least one actuator for controllably moving the linkage assembly and the work tool relative to the work machine, means for determining a force exerted on the work tool, and a controller for receiving a signal from the means for determining a force and responsively determining at least one non-contact force exerted on the work tool, determining a calibration factor as a function of the at least one non-contact force, determining a contact being made between the work tool and the surface, and determining the contact force of the work tool with the surface as a function of the contact being made and the calibration factor.